hugo/tpl/compare/truth.go
Bjørn Erik Pedersen 02eaddc2fb
tpl/tplimpl: Fix template truth logic
Before this commit, due to a bug in Go's `text/template` package, this would print different output for typed nil interface values:

```
{{ if .AuthenticatedUser }}User is authenticated!{{ else }}{{ end }}
{{ if not .AuthenticatedUser }}{{ else }}}User is authenticated!{{ end }}
```

This commit works around this by wrapping every `if` and `with` with a custom `getif` template func with truth logic that matches `not`, `and` and `or`.

Those 3 template funcs from Go's stdlib are now pulled into Hugo's source tree and adjusted to support custom zero values, e.g. types that implement `IsZero`.

This means that you can now do:

```
{{ with .Date }}{{ . }}{{ end }}
```

And it would work as expected.

Fixes #5738
2019-03-06 22:52:38 +01:00

73 lines
2.1 KiB
Go

// Copyright 2019 The Hugo Authors. All rights reserved.
// The functions in this file is based on the Go source code, copyright
// The Go Authors and governed by a BSD-style license.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package compare provides template functions for comparing values.
package compare
import (
"reflect"
"github.com/gohugoio/hugo/common/hreflect"
)
// Boolean logic, based on:
// https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/funcs.go#L302
func truth(arg reflect.Value) bool {
return hreflect.IsTruthfulValue(arg)
}
// getIf will return the given arg if it is considered truthful, else an empty string.
func (*Namespace) getIf(arg reflect.Value) reflect.Value {
if truth(arg) {
return arg
}
return reflect.ValueOf("")
}
// And computes the Boolean AND of its arguments, returning
// the first false argument it encounters, or the last argument.
func (*Namespace) And(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
if !truth(arg0) {
return arg0
}
for i := range args {
arg0 = args[i]
if !truth(arg0) {
break
}
}
return arg0
}
// Or computes the Boolean OR of its arguments, returning
// the first true argument it encounters, or the last argument.
func (*Namespace) Or(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
if truth(arg0) {
return arg0
}
for i := range args {
arg0 = args[i]
if truth(arg0) {
break
}
}
return arg0
}
// Not returns the Boolean negation of its argument.
func (*Namespace) Not(arg reflect.Value) bool {
return !truth(arg)
}